Magnetic blast alternating current circuit interrupter comprising a rectifying arc extinction circuit

ABSTRACT

An alternating current circuit interrupter comprising separable contacts to draw an arc and at least one auxiliary shunt path including series connected rectifiers and a controlled rectifier which can be triggered shortly before current zero in the appropriate current half-cycle. A terminal electrode of the shunt path is disposed adjacent the contacts and magnetic blast means to blow the arc against the electrode only when the current has the instantaneous direction corresponding to the conducting sense of the rectifiers to switch the current to the shunt path. Means may be provided to prevent the stagnation of the arc roots and to permit commutation of the current during any half-cycle to a single or to a double shunt path.

United States Patent 1191 Pelenc et al. July 9, I974 [54] MAGNETIC BLAST ALTERNATING 2,614,232 10/1952 Kalb 317/75 x UPTE 3,633,069 1/1972 Bernard 317/11 B E 3,675,079 7/1972 Labbaye et a1 317/11 E EXTINCTION CIRCUIT [75] Inventors: Yves Pelenc, La Tronche; Georges Exammer jar,nes Trammen Bernard, Saint Egreve, both of Attorney, Agent, or FzrmStevens, Davis, Miller & France Mosher [73] Assignee: Merlin Gerin, Grenoble, France [22] Filed: Mar. 23, 1973 [57] ABSTRACT [21] App!" 344,204 An alternating current circuit interrupter comprising separable contacts to draw an arc and at least one [30] F i A li ti P i it D t auxiliary shunt path including series connected rectifi- Mar 28 1972 France n 7210942 ers and a controlled rectifier wh1ch can be triggered 1972 France 72 45142 shortly before current Zero in the appropriate current 6 '1973 France 64228 half-cycle. A terminal electrode of the shunt path is disposed adjacent the contacts and magnetic blast [52] U S Cl 317/11 A 307/136 317/11 D means to blow the are against the electrode only when 317/75 the current has the instantaneous direction corre- [5]] Int Cl Hozh 7/22 sponding to the conducting sense of the rectifiers to [58] Fieid E H A 11 switch the current to the shunt path. Means may be 6 provided to prevent the stagnation of the arc roots and to permit commutation of the current during any half- [56] References Cited cycle to a single or to a double shunt path. UNITED STATES PATENTS 21 Claims, 15 Drawing Figures 1.179.722 4/1916 Hcinritz 317/75 PATENTEDJUL 9 1 3.823.341

SHEEI 3 0F 4 Fig. 10

MAGNETIC BLAST ALTERNATING CURRENT CIRCUIT INTERRUPTER COMPRISING A RECTIFYING ARC EXTINCTION CIRCUIT This invention relates to alternating current circuit interrupters and more particularly to circuit interrupters comprising a rectifying arc extinction shunt path to which the current can be switched in order to prevent restriking of the are between the main contacts of the circuit interrupter.

A circuit interrupter of this kind is described in U.S. Pat. No. 3,633,069. An arc is drawn between a pair of separating main contacts which are shunted by a circuit consisting of a series arrangement of rectifiers, such as semiconductor diodes, one of the rectifiers being a controlled rectifier, such as a thyristor. Electronic trigger means responsive to the current to be interrupted are provided to fire the thyristor after separation of the main contacts shortly before current zero in the current half-cycle for which the rectifying shunt circuit is in conductive position relative to the instantaneous current so that the current flowing through the opening or fully opened main contacts and the are drawn therebetween is eventually commutated to the shunt path at a moment at which the current has decayed to no more than a small value. Once the arc across the main contacts has been extinguished and until the current drops to zero, the entire current flows through the shunt path and the instant of firing of the controlled rectifier is determined to permit total deionization between the main contacts beforeappearance of the restriking voltage in the next half-cycle. In the next halfcycle a reverse current can flow neither through the shunt path, which is blocked by the rectifiers now in non-conductive position, nor via the main contacts, whose contact gap is sufficiently deionized to inhibit any restriking of an arc. Consequently, the arc is extinguished and the circuit finally interrupted without stressing too much the rectifiers which have to carry only a relatively small current and the number of which is chosen to resist the voltage applied thereto under the most heavy duty conditions. Untimely triggering is prevented by deriving the supply voltage of the trigger device from the arc voltage so that the self-contained trigger device is unable to operate as long as the contacts are closed. It is a matter of course that the main contact structure of the described circuit interrupter should only be designed to withstand the arc current for a short while and that a heavy arc-extinction device can be dispensed with because of the operation of the shunt path which drains the current at the appropriate instant. A second switch or another pair of contacts is connected in series with the first contacts between which an arc is drawn in order to isolate the rectifiers and the first contacts after the arc extinction. The second switch should be in opened position at the moment of the final arc extinction and this condition can be obtained by opening both pairs of contacts at the same time.

For a full understanding of all implications of the present invention reference may be had to the above mentioned U.S. Patent which describes in detail several embodiments of the trigger circuit. It is to be understood that the specific structure and operation of the shunt circuit and of the trigger circuit do not constitute a part of the present invention and that any appropriate arrangement may be retained for these devices, the

present invention being only concerned with the insertion of the whole shunt circuit as such during the opening operation of the circuit interrupter as will become apparent hereinafter.

It has been found that an opening of the main arcing contacts of the switch described in U.S. Pat. No. 3,633,069 during the current half-cycle for which the rectifiers of the shunt path are in non-conductive position may produce, after a first extinction of the arc, an important restriking voltage at the beginning of the next half-cycle. This high overvoltage is due to the small breaking capacity of the main contacts. Although enhancing a rapid transfer of the current to the shunt path, the overvoltage pulse may cause an untimely triggering of the controlled rectifier which renders then the whole shunt path conductive during a major part of the current half-cycle. As a result the rectifiers might be destroyed. French Pat. No. 2,148,760 suggests a remedy for this situation but it has been found that the proposed system tends to produce an asymmetric arc voltage for successive current half-cycles and is too complicated and not sufficiently reliablein all cases.

It is an object of the present invention to provide a circuit interrupter of simple and reliable construction in which the rectifying shunt circuit and more particularly the controlled rectifier thereof is preserved from overvoltages which might cause the untimely triggering thereof.

A related object is to provide an interrupter in which the shunt path is inserted only during the current halfcycle for which the shunt path is in conductive position.

A more general object of the invention is to provide a circuit interrupter of more simple construction than the known interrupters, particularly with respect to the choice of rectifiers of the shunt path and to the design of the isolating device for the shunt path.

A further object of the invention is to provide a circuit interrupter in which the arc roots, pending final extinction of the are, are forced to travel on appropriately arranged arcing horns to prevent a stagnation of the roots and the resulting erosion of the contacts.

Another object of the invention is to provide a circuit interrupter in which the current is commutated to a shunt path during any current half-cycle.

These and other objects, features and advantages will become apparent from the following description of some embodiments which are schematically shown in the accompanying drawings, wherein:

FIG. 1 shows the wave form of a cycle of the current flowing through a circuit interrupter according to the invention, and of the arc voltage;

FIG. 2 and FIG. 3 are schematic representations of two embodiments of the invention;

FIG. 4 shows the main contact zone of a further embodiment;

FIG. 5 is a schematic elevational representation of an embodiment including means to propel the arc roots along arcing horns;

' FIG. 6 is a view taken along line VI-VI of FIG. 5, the arcing horns of the other contact being of identical configuration as seen from the same side;

FIG. 7 is an elevational side view taken along the line .Vll -Vll of FIG. 8 of another arrangement of arcing horns according to the invention;

FIG. 8 is a cross-sectional view taken along line VIII- VIII of FIG. 7, the configuration of the arcing horns of the right hand side contact being substantially identical with the configuration shown in FIG. 7;

FIG. 9 is a partial elevational side view of another arrangement of concentric arcing horns;

FIG. 10 is a partial cross sectional view taken along line X-X of FIG. 9;

FIGS. 11 and 12 show another embodiment in views similar to FIGS. 7 and 8, respectively;

FIG. 13 is a view similar to FIG. 3 of an embodiment having two rectifying shunt paths;

FIGS. 14 and 15 show further embodiments as viewed in FIG. 3 having a single shunt path which may be inserted at any current half-cycle.

In the different figures, corresponding parts are designated by the same reference numerals.

With reference now to FIG. 2, there is shown a circuit interrupter having two electrically seriesconnected pairs of contacts generally designated by the numerals 10 and 12, respectively, constituting the main circuit or current path 14 ofthe apparatus. An auxiliary or shunt circuit 16 comprises a series connection of like poled rectifiers 18, which may be semiconductor diodes, one of which, 20, being a controlled rectifier, such as a thyristor, or SCR having a control gate 22. The gate 22 is controlled by a trigger device 23 which is in turn connected to a current sensing device 25 inserted in the main circuit 14 and to an appropriate volt age supply point 27 of the shunt path 16. The righthand terminal of the shunt path is connected to the main circuit, as shown, and the left-hand terminal comprises an electrode 34, positioned in the region of the main contact pair 12.

The separable contacts 28 and 30 form the isolating contact pair 10 and the separable contacts 24 and 26 form the main arcing contacts which are shown in the final open-circuit position. The movable contacts shown are sliding contacts but it is a matter of course that another type of contacts may be retained, one or both of which being movable. While the contacts shown are simple pressure or butt contacts more sophisticated contact forms may clearly be adopted. In the contact zone of contact pair 12 a unidirectional magnetic field is produced, as schematically shown at 36. In the event, the magnetic field issues from the plane of FIG. 2, perpendicularly thereto and extends laterally sufficiently to cover the entire arc region 32 between the opened contacts and the tip of electrode 34 which is located substantially in the median symmetry plane of the fully opened contacts 24, 26 but axially offset a sufficient distance to permit the magnetic field 36 to urge the are 38 drawn between the contacts 24, 26 against electrode 34 only when the current has a direction, as shown by the arrow I, for which the rectifers 18 are in conductive position, as connected by the electrode 34 to the main circuit 14. The magnetic field 36 may be produced by a permanent magnet or by an electromagnet 37 (FIG. 3) fed by an independent direct current source (not shown) or energized by a rectified current derived from the very current flowing through the circuit interrupter.

The device shown in FIG. 2 operates as follows:

The movable contacts 26 and 30 of the contact pairs 10 and 12 are opened simultaneously in the direction of the arrows by random-time opening means (not shown) to draw an are between the contacts 28 and 30 and another are, 38, between the contacts 24 and 26. Though the opening may take place at any instant in the current cycle it will be assumed that in the event the opening is operated somewhere at the beginning of the half-cycle A (FIG. 1) of the current for which the rectifiers 18 are in non-conductive position, that is at a moment at which the instantaneous current flows in the direction opposite to the direction of arrow I of FIG. 2. The magnetic field 36 urges the are 38 upwards, as viewed in FIG. 2, that is away from the electrode 34 which remains in a non-ionized region. At the time t, the arc current has decayed to zero so that the arc volt age shown in dashed lines passes through zero too. At a time t the arc restrikes in the still ionized arc region whereby the arc voltage reaches a restriking top value U, which cannot affect the shunt circuit 16 however, the latter being still in open circuit at the time 1 The are current flows now in the direction of arrow I (halfcycle B) so that the magnetic field 36 urges the are 38 downwards into engagement with the electrode 34. This electric contact between the electrode 34 and the arc 38 takes place at a time at which the arc voltage has reached a normal value, well below the restriking top U and the number of series-connected rectifiers 18 is chosen to withstand the arc voltage until the extinction thereof. The shunt path 16 is now connected through the electrode 34 and the are 38 to the main contact 24 of the main circuit 14 but no current can as yet be switched to the shunt path as the controlled rectifier 20 is still in blocked condition. At a time determined by a preselected relatively small current value, the triggering device 23 fires the controlled rectifier 20 which turns ON instantly as expounded in more detail in the above cited US. Patent. The right-hand portion of the are burning between the electrode 34 and the contact 26 is extinguished and the current is commutated from the main circuit to the auxiliary circuit 16. At the subsequent current Zero the remaining are portion is also extinguished and a restriking at the next current halfcycle is now excluded as explained in the above cited US. patent.

It is apparent that the rectifiers are protected against the overvoltage of the restriking voltage because the shunt path is only inserted after occurrence of the restriking voltage. This feature is of course conserved if the initial opening of the circuit interrupter takes place at another instant in the current cycle.

It is to be noted that a resistor 50 of appropriate high resistance may be connected between the electrode 34 and the main circuit 14, as shown in dashed lines in FIG. 2, in order to damp out possible transient overvoltage pulses due for instance to a too sudden contact between the arc and the electrode 34.

FIG. 3 shows how the contact pairs 10 and 12 can be merged into a single pair comprising in the shown embodiment a movable sliding contact 30 and a stationary contact 26. The operation of this device is similar to the operation of the device of FIG. 2. Suffice it to say that the partial deionization of the interval between the contacts 30, 26 is sufficiently advanced at current zero at the end of half-cycle B to prevent restriking of the arc across the interval 32 in the next current half-cycle. The deionized interval between the electrode 34 and the contact 30 isolates the shunt circuit from the main circuit after final arc extinction without intervention of a supplementary switch such as contact pair 10 in FIG.

FIG. 4 shows an embodiment in which the main contacts 30, 26 are equipped with arcing horns 40, 42,

respectively, extending generally in the direction of the electrode 34. This arrangement enhances a rapid propelling of the are in the direction of the electrode 34 where the arc is divided in two elementary arcs 44, 46. The electrode 34 may be shaped as a screen to prevent a detrimental ionization of the interval between electrode 34 and contact 42 after extinction of the arc 46 by the still burning are 44. A screen 48 of insulating material (shown in dashed lines in FIG. 4) may prolong the electrode 34 to further impede this effect.

FIGS. 5 and 6 show a circuit interrupter having the same general electric connection diagram as the apparatus represented in FIG. 3. The arcing horns 40, 42 however have a different configuration to prevent the arc roots from dwelling on the same spot causing thereby a detrimental erosion. Both horns being of identical shape, as viewed from the same side, only one of them, arcing horn 40, will now be described. The arcing horn 40 comprises a ring-shaped, generally circular end portion 52 connected by a tangential, generally vertical leg 54 to the region immediately adjacent the contact 30 but separated therefrom by a small gap 55. Another gap 56 separates the extreme end of the horn 40 from the vertical leg 54. The magnetic field 36 tending to propel the arc in the proper direction is produced by a number of permanent magnets 58, 59, 60, 62 which act on the left are root (as viewed in FIG. 5), similar conditions existing at the other horn 42. As a matter of fact, it suffices to act on the arc roots in order to propel the entire arc in the appropriate direction. As viewed in FIG. 6, all permanent magnets have upper pole faces of the polarity indicated on FIG. 6 and which are substantially flush with the upper side of the arcing horn 40 so that the magnetic lines of force issuing from the upper north poles of the magnets 58, 59 pass over the (upper) arc root face of horn portions 52, 54 to rejoin and disappear into the (upper) south poles of the magnets 60 and 62 as shown by arrows 57. Of course, the magnetic lines of force are oppositely directed on the lower side of the arcing horn 40, that is beneath the plane of FIG. 6 but this circumstance is without interest as the arc roots are only subjected to the magnetic field existing at the other side of the horns. It will be clear that the arc roots attached to arcing horns 40 and 42 will be propelled downwardly in the direction of arrow 61 during the current half-cycle for which the diodes 18, are in conductive position whereby the concentric arrangement of the magnets 59 and 62 causes the arc root to continuously rotate along the closed loop portion 52 of the arcing horn 40. This continuous motion of the arc root avoids a local heating of a part of the arcing horn on which the root would dwell otherwise. A local intense ionization is also prevented by the arrangement shown.

Two further upper arcing horns 64, 66 are arranged in radial symmetry with respect to horns 40, 42 to guide the arc roots upwardly, away from contacts and 26, during the current half-cycle for which the diodes 18, 20 are in nonconductive position. Parts 70 and 68 correspond to parts 54 and 52 of horn gaps 65 and 78 to gaps 55 and 56, and magnets 74, 75, 72 and 76 to magnets 58, 59, 60 and 62, respectively, the polarity of the magnets being of course inverted.

The device shown in FIGS. 5 and 6 operates as follows:

After separation of the contacts 26 and 30 during the current half-cycle A for which the rectifiers 18, 20 are nonconductive, an arc is drawn and the roots of the are are propelled upwardly along the leg 70 by the magnetic field 36 produced by the magnets 72 and 74. Eventually, the arc roots are blasted by the magnetic field of the magnets 75 and 76 along the circular path 68 of the horns 64, 66 and the roots perform rapidly one or several turns along the path 68, jumping across the gap 78. As long as the current does not change direction, a downwards movement along the leg 70 is prevented by the field produced by the magnets 72 and 74. After the passage of the current through zero the arc restrikes in the ionized region between the arcing horns 64, 66 whereby the current flows in the opposite direction (half-cycle B). The current sense being inverted, the roots are now propelled in the direction opposite to the direction of the arrow shown in horn 64 so that the roots jump rapidly over the gap 65, the contact 30 and the gap 55 to travel along the leg 54 and the circular path 52 in the direction of the arrow 61. The gap 78 may also be effective to enhance the movement of the root initially attached to the arcing horn portion 68 in the right direction. As soon as the arc roots engage the portion 52 of arcing horns 40 and 42, the middle portion of the arc engages the electrode 34 which may also comprise a circular path although a dwelling of the intermediate arc roots on electrode 34 is practically excluded by the continuous motion of the end roots of the are travelling along the circular paths 52. The final arc extinction proceeds as explained hereinabove with reference to FIG. 2.

It is to be noted that in case the arc extinction does not take place at current zero for one reason or another, the restriking of an arc in the ionized region between the arcing homs 40, 42 is immediately followed by a rapid propelling of the arc in the direction of the upper horns 64, 66 leaving the electrode 34 and the shunt circuit 16 in open circuit position so that the thyristor 20 cannot be untimely triggered. The final extinction may then occur at the next half-cycle, as stated above.

FIGS. 6 and 8 show an embodiment in which the closed loop portions of the arcing horns are concentric. The movable contact 38 is now tubular and surrounds a permanent magnet 82 having a north pole directed towards the stationary contact 84 which is also ringshaped to surround a permanent magnet 86 of opposite polarity. A coplanar outer annular arc root path 88, 90 is also associated with the contacts 30 and 84, respectively, to guide the arc roots during the current halfcycle for which the shunt path is conductive. Transverse, more or less radial extensions 92, 94 of the semicircular segments 88 and 90 extend towards the inner paths and are separated therefrom by gaps 96. In turn, the inner semi-circular segments 80 have transverse, more or less radial extensions 98, I80 directed towards the outer paths 88, 90, from which they are separated by gaps 102. In a manner similar to the arrangement of FIG. 6, the segments 88 and the segments 80 are separated by air gaps 106. A ring of permanent magnets 184 surround the outer paths 88, and cooperate with the central permanent magnet of opposite polarity in a manner similar to the arrangement shown in FIG. 6, the polarities being as shown in FIGS. 7 and 8. Permanent magnets 108 and 1110 are associated with the legs 92, 94, 98 and 108 to cause the are roots to travel along these legs in the appropriate direction.

The operation of the device of FIGS. 7 and 8 is similar to that of FIGS. and 6. After drawing of an are between the contacts 84 and 30, the left-hand arc root of the arc is transferred to the inner circular path 80 as soon as the movable contact 30 is withdrawn therefrom. The are root starts immediately to rotate along the path 80 in the direction of the arrow, jumping across the gaps 106, as long as the direction of the current corresponds to the non-conductive relative position of shunt path 16. The arc roots cannot escape along the extensions 98, 100 because of the magnetic field produced by magnets 108, 110. In the embodiment shown, the effective polarity of permanent magnet 86 is opposite to the polarity of magnet 82 so that the arc roots attached to the inner paths 80 and 84 rotate in opposite directions. Of course, a rotation in the same direction may be obtained by inversion of the polarity of one of the magnets (and of the corresponding outer ring magnets). As soon as the arc current is inverted in the next half-cycle the arc roots start to move outwardly along the legs 98 or 100 to travel along the outer ring-shaped paths 88, 90 whereby the left-hand arc root moves in the direction of the arrow shown in FIG. 7 as a result of the action of magnets 104 and 82. The middle part of the arc engages the annular discshaped electrode 34 and the arc extinction proceeds then as has been explained herein above. In case the arc is not definitively interrupted, the legs 92, 94 permit the arc roots during the next half cycle to return to the inner path 80. The gaps 96, 102 and 106 sustain the action ofthe magnetic field and constitute barriers preventing the arc from moving in the wrong direction.

FIGS. 9 and show a modified form of the embodiment of FIGS. 7 and 8 in a partial representation. The movable contact 30 constitutes now itself the circular inner path for the arc root during the current half-cycle for which the rectifiers of the shunt path are in nonconductive position. The radial legs 112 are regularly spaced apart along the circumference of the outer arcing horn portion 88 of which they constitute radial inner extensions. Each extension may have a truncated conical shape, as shown, and is sandwiched by a pair of permanent magnets 114 disposed with opposite polarities and which protrude from the arc root surface of the radial legs 112. The legs are, as all the other parts of the arcing horn portions of conductive material and the permanent magnets are magnetically connected by yoke portions 116 of ferromagnetic material to increase the effective magnetic field along the arc root faces of the legs 112. Gaps 118 separate the inner end portions of the legs 112 from the outer surface of the tubular contact member 30 which surrounds again, as in the embodiment shown in FIGS. 7 and 8, the permanent magnet 82. The operation of this embodiment is similar to the operation of the device of FIGS. 7 and 8. The left-hand arc root rotates on the inner path 30 in the direction of the arrow shown in FIG. 9 as long as the current flows in a direction excluding its transfer to the shunt path. After inversion of the direction of the current, the root moves along one of the legs 112 towards the outer ring 88 along which the arc root travels in the direction of the shown arrow. An inversion of the direction of the current in the other sense causes the arc root to move inwardly along one of the legs 112.

FIGS. 11 and 12 show an embodiment in which the different guide parts for the arc roots are arranged in a coaxial dome-shaped manner. The circular end portion of the tubular movable contact 30 cooperates with an annular stationary contact 84 and permanent magnets 82 and 86 are disposed within the contacts, respectively. The polarities of the magnets are chosen, as shown, to cause a rotation of the arc roots in the direction of the arrow shown on FIG. 12. The outer paths are formed by coaxial cylindrical surfaces 120 and 122 whereby the latter may be constitued by the outer surface of the tubular contact 30, as shown. The electrode 34, itself of cylindrical form, is inserted between the cylindrical surfaces 120 and 122 and permanent magnets 124 producing a rotation of the outer arc root in the direction of the arrow are disposed on both sides of the outer path 120, as shown. Transverse legs 126 connect the inner path 84 to the outer path 120 to permit a transfer of the corresponding arc root in both directions under the action of permanent magnets 128.

The embodiments shown in FIGS. 13 to 15 permit a switching of the current flowing through the main circuit of the circuit interrupter to a shunt path during any current half-cycle, whatever may be the instantaneous current direction. Corresponding duplicate parts are designated in these FIGURES by the same reference character as the parent parts but a prime mark is affixed to the reference character of the duplicate part.

In the embodiment shown in FIG. 13, which is to be compared to the device represented in FIG. 3, a second auxiliary or shunt circuit 16 of identical composition as the shunt circuit 16 has its right terminal connected to the main circuit while the left terminal comprises an electrode 34' which is located in the region of the contacts 30 and 26 symmetrically to the other electrode 34 with respect to the contacts. It will be understood that the unidirectional magnetic field 36 blasts the arc upwardly against the electrode 34 if the instantaneous current flows in the direction of the arrow 1' and downwardly against the electrode 34 if the current flows in the opposite direction indicated by the arrow I. In any case, one and only one of the shunt circuits 16, 16' is thus inserted and a subsequent triggering of the corresponding thyristor 20 or 20' causes the final interruption as explained hereinabove.

The same result can be obtained with the aid of a single shunt circuit as shown in FIGS. 14 and 15. In the embodiment of FIG. 14, each contact is associated with a pair of oppositely directed arcing horns 40, 40 and 42, 42', respectively. A pair of electrodes 130, 132 connected by conductors 136 and 142 to the terminals 134 and 140, respectively, of the auxiliary circuit 16 is disposed between the end portion of horns 40, 42 and a similar pair of electrodes 132', cross-connected by conductor 144 and 138 to the terminals and 134, respectively, is disposed between the arcing horns 40' and 42. It will be clear that an arc in which the current flows in the direction of the arrow I is urged by the magnetic field 36 towards the electrodes 130' and 132 which divide the arc in three elementary arcs 146, 148 and 150. The voltage of the are 148 is applied to the shunt circuit 16 in the right direction so that the subsequent firing of the thyristor 20 diverts the current to the shunt path 16 thereby extinguishing the elementary are 148. After passage through zero of the current the other elementary arcs 146, 150 are also extinguished producing a final interruption of the current. Of course, in case the initial arc current flows on opening of the contacts in the opposed direction, the arc is blasted against the electrodes 130, 132, which again apply the arc voltage in the right direction to the shunt circuit. The same result may be obtained with the arrangement of FIG. having two series connected separable contact pairs comprising the contacts 30, 26 and 30', 26, respectively. The unidirectional magnetic field 36' produced in the region of contacts 30', 26' has a direction opposite to the direction of the magnetic field ex isting between the contacts 30, 26. The terminal 134 of the shunt path 16 is connected, as in FIG. 3, to the electrode 34, but in the event also to an electrode 152 disposed slightly'beneath the contacts 30 and 26, as shown. Similarly, the terminal 140 of the shunt circuit 16 is connected to an upper electrode 34 located above the contacts 30, 26 and to asecond upper electrode 152' positioned above the contacts 30' and 26, substantially symmetrically with respect to electrodes 34 and 152, respectively. It will be apparent that the arcs drawn between the contacts 30 and 26 and 30' and 26' will be blasted by the magnetic fields'36 and 36 in the direction of the electrodes 34' and 152, respectively, if the current immediately after opening of the contacts 30, 26 and 30', 26 flows in the direction of the arrow I. If the current flows in the opposite sense,

the arcs are blasted against electrodes 34 and 152'. In both cases the shunt path 16 is in the right position to receive the arc current which is eventually interrupted at the end of the half-cycle as set forth hereinabove.

What is claimed is: i

1. An alternating current circuit interrupter comprismg:

a main circuit including separable contact means adapted to draw an arc;

an auxiliary circuit having series connected like poled semiconductor rectifier means including controlled rectifier means, said auxiliary circuit comprising terminal electrode means disposed adjacent said contact means;

magnetic blast means producing a magnetic field in the region of said are and tending tomagnetically blast said are against said electrode means only during the current half-cycle for which said rectifier means, as connected by said electrode means, are in conducting position for the current flowing through said circuit interrupter; and

trigger means responsive to said current to fire, subsequently to separation of said contact means and to electric contact of said are with said electrode means, said controlled rectifier means shortly before current zero in said half-cycle thereby to commutate the current flowing through said main circuit to said auxiliary circuit.

2. A circuit interrupter according to claim 1, said contact means comprising-a pair of separable contacts, said electrode means comprising an electrode disposed substantially in the median plane of said contacts in the open circuit position thereof. 1

3. A circuit interrupter according to claim 2, said electrode being transversely offset between said contacts.

4. A circuit interrupter according to claim 3, said contacts comprising arcing horns to enhance the movement of said are in the direction of said electrode.

5. A circuit interrupter according to claim 1, said magnetic blast means comprising permanent magnet means.

6. A circuit interrupter according to claim 1, said magnetic blast means comprising an electromagnet energized by the current flowing through said circuit interrupter.

7. A circuit interrupter according to claim 6, said magentic blast means further comprising rectifier means to rectify the energizing current of said electromagnet.

8. A circuit interrupter according to claim 1, said auxiliary circuit comprising a resistor to damp the transient voltage applied to said rectifier means.

9. A circuit interrupter according to claim 1, further comprising arcing horn means of conducting material to guide the roots of said arc, said arcing horn means having a first portion providing for at least one root of said arc at least one path extending from said contact means in the general direction of said electrode means, and a second portion providing for said roots paths extending from said contact means and which are spatially arranged in such a manner relative to said electrode means as to keep the are having the roots thereof dwelling on said second portion away from said electrode means, said magnetic blast means being adapted to propel said at least one root along said first portion during said current half-cycle, and said roots along said second portion during the current half-cycle of opposite polarity.

10. A circuit interrupter according to claim 9, at least one of said first and second portions of said arcing horn means comprising a closed loop path associated with further magnetic blast means tending to cause the corresponding root of said arc to move continuously along said closed loop path during the corresponding current half-cycle.

11. A circuit interrupter according to claim 10, said closed loop path having a gap tending to prevent the dwelling'of the corresponding root on said closed loop path after inversion of the direction of the current.

12. A circuit interrupter according to claim it), said contact means comprising a pair of separable contacts, each contact being associated with a pair of arcing horns directed away from said contact in opposite directions and ending each in a semi-closed loop portion, said further magnetic blast means comprising for each horn permanent magnets surrounded by and surrounding the loop portion thereof, respectively.

13. A circuit interrupter according to claim 10, said contact means comprising a pair of separable contacts,

said first and second portions comprising an outer and an inner annular path, respectively, arranged substantially concentrically around said contacts, said electrode means comprising an annular electrode positioned outwardly of said inner path, said arcing horn means comprising at least one guide leg extending transversely between said paths to permit the transfer of the corresponding arc root between said annular paths.

M. A circuit interrupter according to claim 13, each contact being associated with a pair of coplanar concentric annular arcing horn portions, each arcing horn portion being divided into a plurality of circle segments ending in a coplanar leg transversely directed towards the other horn portion and separated therefrom by a gap.

15. A circuit interrupter according to claim 14, said magnetic blast means comprising permanent magnets arranged adjacent said leg and adapted to propel an arc root attached to said leg in the appropriate direction therealong taking into account the instantaneous direction of the arc current, said further magnetic blast means comprising permanent magnets arranged concentrically adjacent said annular arcing horn portions, respectively, to cause an arc root attached to said horn portions to move therealong.

16. A circuit interrupter according to claim 13, said inner annular path being comprised of one of said contacts.

17. A circuit interrupter according to claim 13, said arcing horn means being arranged in a generally domeshaped manner.

18. A circuit interrupter according to claim 1, said contact means comprising a pair of separable contacts, said electrode means comprising electrodes disposed on both sides of the zone in which said arc is initially drawn, said electrodes being positioned and connected to said auxiliary circuit in a manner such that said current flowing through said main circuit can be commutated to said auxiliary circuit for both directions of said current pursuant to electric contact of said arc with the electrodes disposed on one side or the other of said zone under the action of said magnetic field.

19. A circuit interrupter according to claim 1, said contact means comprising two series connected pairs of separable contacts adapted to draw an arc therebetween, said electrode means comprising electrodes disposed adjacent each of said pairs of contacts, said magnetic blast means producing a magnetic field in the region of each arc and tending to magnetically blast both arcs against predetermined electrodes according to the instantaneous direction of said current, said electrodes being positioned and connected to said auxiliary circuit in such a manner that the current flowing through said main circuit can be commutated to said auxiliary circuit for both directions of said current pursuant to electric contact of said arcs with said electrodes.

20. An alternating current circuit interrupter comprising:

a main circuit including a pair of separable contacts adapted to draw an arc therebetween;

a pair of electrodes disposed adjacent said contact means substantially on opposite sides of the zone in which said are is initially drawn;

magnetic blast means to produce a magnetic field in the region of said arc and tending to magnetically blast said are against one or the other of said electrodes according to the instantaneous direction of the arc current;

a pair of auxiliary circuits having each series connected like poled semiconductor rectifier means including controlled rectifier means, said auxiliary circuits being connected to said electrodes, respectively, and to said main circuit in such a manner that each auxiliary circuit is in conducting position for the instantaneous current flowing through said circuit interrupter as the electrode thereof is in electric contact with said arc pursuant to the action of said magnetic blast means;

and trigger means responsive to the instantaneous value of said current to fire, subsequently to separation of said contacts and to electric contact of said arc with one of said electrodes, said controlled rectifier means of the corresponding auxiliary circuit shortly before current zero in the corresponding half-cycle of the current, thereby to commutate the current flowing through said main circuit to one or the other of said auxiliary circuits according to the instantaneous direction of the current.

21. An alternating current circuit interrupter comprising:

a main circuit including separable contact means adapted to draw an arc;

magnetic blast means producing a unidirectional magnetic field in the region of said arc to magnetically blast said arc according to the instantaneous direction of the arc current in a first direction substantially transverse of the initial direction of said are or in a direction opposed to said first direction; and

a rectifying shunt circuit having terminal electrode means disposed adjacent said contact means in such a manner that the current flowing through said main circuit can be commutated to said shunt circuit pursuant to electric contact of said are with said electrode means only if said current has a direction corresponding to the conducting sense of said rectifying circuit. 

1. An alternating current circuit interrupter comprising: a main circuit including separable contact means adapted to draw an arc; an auxiliary circuit having series connected like poled semiconductor rectifier means including controlled rectifier means, said auxiliary circuit comprising terminal electrode means disposed adjacent said contact means; magnetic blast means producing a magnetic field in the region of said arc and tending to magnetically blast said arc against said electrode means only during the current half-cycle for which said rectifier means, as connected by said electrode means, are in conducting position for the current flowing through said circuit interrupter; and Trigger means responsive to said current to fire, subsequently to separation of said contact means and to electric contact of said arc with said electrode means, said controlled rectifier means shortly before current zero in said half-cycle thereby to commutate the current flowing through said main circuit to said auxiliary circuit.
 2. A circuit interrupter according to claim 1, said contact means comprising a pair of separable contacts, said electrode means comprising an electrode disposed substantially in the median plane of said contacts in the open circuit position thereof.
 3. A circuit interrupter according to claim 2, said electrode being transversely offset between said contacts.
 4. A circuit interrupter according to claim 3, said contacts comprising arcing horns to enhance the movement of said arc in the direction of said electrode.
 5. A circuit interrupter according to claim 1, said magnetic blast means comprising permanent magnet means.
 6. A circuit interrupter according to claim 1, said magnetic blast means comprising an electromagnet energized by the current flowing through said circuit interrupter.
 7. A circuit interrupter according to claim 6, said magentic blast means further comprising rectifier means to rectify the energizing current of said electromagnet.
 8. A circuit interrupter according to claim 1, said auxiliary circuit comprising a resistor to damp the transient voltage applied to said rectifier means.
 9. A circuit interrupter according to claim 1, further comprising arcing horn means of conducting material to guide the roots of said arc, said arcing horn means having a first portion providing for at least one root of said arc at least one path extending from said contact means in the general direction of said electrode means, and a second portion providing for said roots paths extending from said contact means and which are spatially arranged in such a manner relative to said electrode means as to keep the arc having the roots thereof dwelling on said second portion away from said electrode means, said magnetic blast means being adapted to propel said at least one root along said first portion during said current half-cycle, and said roots along said second portion during the current half-cycle of opposite polarity.
 10. A circuit interrupter according to claim 9, at least one of said first and second portions of said arcing horn means comprising a closed loop path associated with further magnetic blast means tending to cause the corresponding root of said arc to move continuously along said closed loop path during the corresponding current half-cycle.
 11. A circuit interrupter according to claim 10, said closed loop path having a gap tending to prevent the dwelling of the corresponding root on said closed loop path after inversion of the direction of the current.
 12. A circuit interrupter according to claim 10, said contact means comprising a pair of separable contacts, each contact being associated with a pair of arcing horns directed away from said contact in opposite directions and ending each in a semi-closed loop portion, said further magnetic blast means comprising for each horn permanent magnets surrounded by and surrounding the loop portion thereof, respectively.
 13. A circuit interrupter according to claim 10, said contact means comprising a pair of separable contacts, said first and second portions comprising an outer and an inner annular path, respectively, arranged substantially concentrically around said contacts, said electrode means comprising an annular electrode positioned outwardly of said inner path, said arcing horn means comprising at least one guide leg extending transversely between said paths to permit the transfer of the corresponding arc root between said annular paths.
 14. A circuit interrupter according to claim 13, each contact being associated with a pair of coplanar concentric annular arcing horn portions, each arcing horn portion being divided into a plurality of circle segments ending in a coplanar leg transversely directed towards the other horn portion and separated therefrom by a gap.
 15. A circuit interrupter according to claim 14, said magnetic blast means comprising permanent magnets arranged adjacent said leg and adapted to propel an arc root attached to said leg in the appropriate direction therealong taking into account the instantaneous direction of the arc current, said further magnetic blast means comprising permanent magnets arranged concentrically adjacent said annular arcing horn portions, respectively, to cause an arc root attached to said horn portions to move therealong.
 16. A circuit interrupter according to claim 13, said inner annular path being comprised of one of said contacts.
 17. A circuit interrupter according to claim 13, said arcing horn means being arranged in a generally domeshaped manner.
 18. A circuit interrupter according to claim 1, said contact means comprising a pair of separable contacts, said electrode means comprising electrodes disposed on both sides of the zone in which said arc is initially drawn, said electrodes being positioned and connected to said auxiliary circuit in a manner such that said current flowing through said main circuit can be commutated to said auxiliary circuit for both directions of said current pursuant to electric contact of said arc with the electrodes disposed on one side or the other of said zone under the action of said magnetic field.
 19. A circuit interrupter according to claim 1, said contact means comprising two series connected pairs of separable contacts adapted to draw an arc therebetween, said electrode means comprising electrodes disposed adjacent each of said pairs of contacts, said magnetic blast means producing a magnetic field in the region of each arc and tending to magnetically blast both arcs against predetermined electrodes according to the instantaneous direction of said current, said electrodes being positioned and connected to said auxiliary circuit in such a manner that the current flowing through said main circuit can be commutated to said auxiliary circuit for both directions of said current pursuant to electric contact of said arcs with said electrodes.
 20. An alternating current circuit interrupter comprising: a main circuit including a pair of separable contacts adapted to draw an arc therebetween; a pair of electrodes disposed adjacent said contact means substantially on opposite sides of the zone in which said arc is initially drawn; magnetic blast means to produce a magnetic field in the region of said arc and tending to magnetically blast said arc against one or the other of said electrodes according to the instantaneous direction of the arc current; a pair of auxiliary circuits having each series connected like poled semiconductor rectifier means including controlled rectifier means, said auxiliary circuits being connected to said electrodes, respectively, and to said main circuit in such a manner that each auxiliary circuit is in conducting position for the instantaneous current flowing through said circuit interrupter as the electrode thereof is in electric contact with said arc pursuant to the action of said magnetic blast means; and trigger means responsive to the instantaneous value of said current to fire, subsequently to separation of said contacts and to electric contact of said arc with one of said electrodes, said controlled rectifier means of the corresponding auxiliary circuit shortly before current zero in the corresponding half-cycle of the current, thereby to commutate the current flowing through said main circuit to one or the other of said auxiliary circuits according to the instantaneous direction of the current.
 21. An alternating current circuit interrupter comprising: a main circuit including separable contact means adapted to draw an arc; magnetic blast means producing a unidirectional magnetic field in the region of said arc to magnetically blast said arc according to the instantaneOus direction of the arc current in a first direction substantially transverse of the initial direction of said arc or in a direction opposed to said first direction; and a rectifying shunt circuit having terminal electrode means disposed adjacent said contact means in such a manner that the current flowing through said main circuit can be commutated to said shunt circuit pursuant to electric contact of said arc with said electrode means only if said current has a direction corresponding to the conducting sense of said rectifying circuit. 